The field of the disclosure relates generally to fiber communication networks, and more particularly, to optical access networks utilizing wavelength division multiplexing.
Telecommunications networks include an access network through which end user subscribers connect to a service provider. Some such networks utilize fiber-optic distribution infrastructures, which have historically provided sufficient availability of fiber strands such that dissimilar types of optical transport signals are carried over their own different fibers. Bandwidth requirements for delivering high-speed data and video services through the access network, however, is rapidly increasing to meet growing consumer demands. As this signal capacity demand continues to grow, the capacity of individual long access fiber strands is limited. The cost of installing new long access fibers is expensive, and dissimilar optical transport signals, unless they are purposely isolated, experience interference from one another on the same fiber strand. This legacy fiber environment requires operators to squeeze more capacity out of the existing fiber infrastructure to avoid costs associated with having to retrench new fiber installment.
Conventional access networks typically include six fibers per node, servicing as many as 500 end users, such as home subscribers, with two of the fibers being used for downstream and upstream residential transport, and the remaining used for node splitting or businesses services. Conventional nodes cannot be split further using conventional techniques, and do not typically contain spare (unused) fibers, and thus there is a need to utilize the limited fiber availability in a more efficient and cost-effective manner. Dense Wavelength Division Multiplexing (DWDM) environments, for example, are capable of multiplexing signals using similar optical transport techniques. In certain access network environments such as the cable television environment, DWDM is able to utilize different formats, but its fiber strand availability is still limited by conventional fiber-optic infrastructure costs and considerations. Cable access networks include analog modulation of the cable RF spectrum onto optical carriers, baseband digital modulation of an optical carrier supporting business services, and Ethernet passive optical network (EPON) and Gigabit passive optical network (GPON) systems carrying data for residential or business subscribers. Each of these different optical transport signals typically requires its own dedicated long fiber strands.
Coherent technology has been proposed as one solution to meet the ever increasing signal traffic demand for WDM-PON optical access networks, in both brown and green field deployments, particularly with respect to long and metropolitan links for achieving high spectral efficiency (SE) and higher data rates per channel. Coherent technology in long optical systems typically requires significant use of high quality discrete photonic and electronic components throughout the access network, such as digital-to-analog converters (DAC), analog-to-digital converters (ADC), and digital signal processing (DSP) circuitry such as an application-specific integrated circuit (ASIC) utilizing CMOS technology, to compensate for noise, drift, and other factors affecting the transmitted channel signals over the access network. Furthermore, as the number of end users per optical fiber increases, so does the cost, and power requirements, of implementing all of these electronic components for each terminal device in the network. Some known proposed coherent solutions have also required their own dedicated long fiber strands to avoid interference from dissimilar optical transport signals. Accordingly, a solution is desired that allows dissimilar transport signals to coexist on the same transmission fibers.